NPB%20112%2009%20resting%20and%20action%20potential%20slides

NPB%20112%2009%20resting%20and%20action%20potential%20slides...

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1 I. The neuron II. Resting membrane potential A. due mainly to K+ efflux: Nernst B. influenced by Na+ : GHK Equation C. Na+/K+ exchange III. Action Potential Outline 9/29/09 Figure 2.2
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2 Outside Inside Na+ Cl- K+ 20 mM 440 mM K+ Cl- Na+ 400 mM 50 mM A- Cell membrane Outside Inside Na+ Cl- K+ 440 mM K+ Cl- Na+ 50 mM A- Cell membrane Make membrane SELECTIVELY permeable to K+ K+ wants to move toward region of lower concentration ( chemical force to move down concentration gradiant)
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3 Outside Inside Na+ Cl- K+ 20 mM 440 mM K+ Cl- Na+ 50 mM A- Cell membrane - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + + + + + + + + + + + + + + + + + + + + + + + + + + As K+ leaves cell, negativity increases on inside of membrane, electrostatically attracts K+. This electrostatic force prevents K+ from leaving cell K+ Channel, Fig. 4.8 c
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4 K+ Na+ Cloud of waters of hydration surrounding K+ ion is smaller due to weaker electrostatic pull of K+ (even though K+ nucleus is larger than Na+) Width of ion channel Ion Selectivity K+ Na+ Ion Selectivity Fits through Bounces off
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5 Outside Inside Na+ Cl- K+ 20 mM 440 mM K+ Cl- Na+ 50 mM A- Cell membrane - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + + + + + + + + + + + + + + + + + + + + + + + + + + Chemical driving force is eventually balanced by Electrical driving force so no further net move- ment of K+ Equilibrium Potential When chemical driving force = electrostatic driving force, NO net movement of K+ = equilibrium The electrical potential (amount of build-up of negativity on inside of cell membrane) that equals the chemical
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